Optical fiber tape cores each of which is formed of a bundle of plural optical fiber cores united together are known for many years. Owing to the merit that a number of optical fibers can be connected all together, these optical fiber tape cores are widely used as optical transmission media in optical communications systems as a result of the rapid introduction of optical fiber cables in subscribers' systems in recent years.
An optical fiber tape core is required to have higher separability into single cores and higher strength, and active research and development work is under way in various companies. To provide optical fiber cores with both strength and separability into single cores, it is the common practice to form a coating layer in a two-layer construction—one being a primary coating layer uniting plural optical fiber cores together and the other a secondary coating layer uniting together such multi-core units covered with such primary coating layers, respectively—and to form the primary and secondary coating layers with UV curable resins different in strength and hardness.
In general, optical fiber tape cores coated with such UV curable resins are fabricated using acrylic materials. The resulting optical fiber tape cores are, however, accompanied by a problem in that they are not sufficient in hardness, durability and flexibility and tend to become loose or break, for example, when twisted. Concerning flexibility, on the other hand, these optical fiber tape cores also involve a problem in that they are extremely weak to bending in the direction of the cores and becomes loose or break although they have durability to folding.
Further, optical fiber tape cores coated with general UV curable resins are also accompanied by a further problem in that they are poor in shape restorability due to their plasticity attributable to the materials and, when wound on bobbins or the like upon storage, they continue to retain a wound shape, in other words, they develop curling and in actual work, for example, upon conducting connection to connectors or the like or performing installation work, this retention of a wound shape (curling) makes it difficult to handle them, resulting in poor workability.
Turning now to a process for the fabrication of optical fiber tape cores, the conventional fabrication of an optical fiber tape core has been conducted generally by the facilities illustrated in FIG. 22. Described specifically, an optical fiber tape core is fabricated by guiding plural optical fiber cores 2a-2h from a core feeder 16 to a core aligner 17 to align the individual optical fiber cores in parallel with each other along a line, introducing the thus-aligned individual optical fiber cores into a coating jig 18, coating the optical fiber cores all together around themselves with a coating material while filling the coating jig 18 with the coating material, feeding out the coated optical fiber cores through a hole of the coating jig 18, and then curing the coating material by a curing means 19 such as a UV irradiation unit. A typical coating jig is illustrated in FIG. 23. The coating jig 18 is constructed of an optical fiber feed-in hole 18a through which the optical fibers 2a-2h are inserted, a coating material reservoir 18b in which a coating material is filled, and an optical fiber feed-out hole 18c through which the optical fiber cores are fed out.
According to this process, however, it is necessary to keep the interior of the coating jig always filled with the coating material, leading to a problem that the material is wasted. This problem involves another problem in that to change the thickness and/or width of an optical fiber tape, a new coating jig equipped with a different hole for feeding optical fiber cores therethrough is needed, thereby making it difficult to readily change the thickness and/or width of the optical fiber tape.
In the above described process, it is also necessary to feed plural optical fiber cores, which are before their formation into a tape and are single cores in a loose state, through the aligner 17 while aligning them with each other and then to insert them into the very small holes (18a and 18c) of the coating jig 18. This setting of the optical fiber cores is troublesome and time-consuming, leading to a reduction in work efficiency. With respect to a demand for the fabrication of a short-distance optical fiber tape core or the formation of an optical fiber tape core into a tape only at a necessary position, the fabrication facilities are difficult to meet such a demand because the distance from the core feeder 16 to the curing unit 19 is tong and fabrication conditions such as the coat thickness do not become constant shortly after an initiation of fabrication.
When fabricating a short-distance optical fiber tape core, forming an optical fiber tape core into a tape only at a necessary position or reinforcing an optical fiber tape core only at a part thereof, it is strongly required to provide the optical fiber tape core with a thicker coating layer, a wider coating layer or the like especially from the standpoint of protection of the optical fibers to be wired within a system. However, the above-described conventional process can by no means meet or is difficult to meet these requirements.
From the standpoint of protecting optical fibers drawn out of optical connectors or an optical component, it is strongly required to form them into a tape. The above-described process is, however, accompanied by a problem in that the tape formation can be hardly effected. The above-described process involves a further problem in that, when optical fibers are wired in a very narrow place, it cannot effect the tape formation.
The present invention has been completed to resolve such problems of the conventional technology as described above. Specifically, an object of the present invention is to provide an optical fiber tape core, which has excellent strength and good flexibility and hardly retains a wound shape (curling).
Another object of the present invention is to provide a process for the fabrication of an optical fiber tape core, which can coat plural optical fiber cores all together in a simple manner. A further object of the present invention is to provide a process for the fabrication of an optical fiber tape core, which can feed a coating material to optical fiber cores only as much as required, can feed a coating material even when the area to be coated extends over a short distance or is partial, can feed a coating material even when optical fiber cores to be coated are wired in a very narrow place, or can feed a coating material to optical fiber cores to form it into a tape while controlling the thickness and/or width of the coating of the tape. A still further object of the present invention is to provide a process for the fabrication of an optical fiber tape core, which can simplify the setting of plural optical fiber cores, can apply a coating over a short distance or on a partial area without wasting a coating material, or can also form into a tape plural optical fiber cores provided at one ends or both ends thereof with optical components such as optical connectors.